The present disclosure relates to a cleaning device cleaning a toner remained on an image carrier and an image forming apparatus including this cleaning device.
In an image forming apparatus, such as a copying machine and a printer, an electrostatic latent image formed on a photosensitive drum is developed to a toner image by a developing device. The developed toner image is transferred onto a transferred medium, such as a sheet, from the photosensitive drum. At this time, the toner image may not be transferred perfectly and may be remained on the photosensitive drum. To the photosensitive drum, discharge product produced when the electrostatic latent image is formed on photosensitive drum may be adhered. Such remained toner and discharge product may interfere with new image forming and may cause transfer failure.
By contrast, the image forming apparatus is provided with a cleaning device removing the remained toner and the discharge product adhered to the photosensitive drum. The cleaning device includes a cleaning roller coming into contact with the photosensitive drum and rotating.
The cleaning roller not only removes adhered substance from the photosensitive drum, but also carries a toner layer to grind a surface of the photosensitive drum by the toner layer. In order to let the cleaning roller carry the toner layer, the toner scraped from the photosensitive drum is collected by a toner layer forming member and the toner is fed from the toner layer forming member to the cleaning roller.
Incidentally, the image forming apparatus is configured so that, in a case where the transferred media is a cardboard, considering strength of stiffness of the cardboard, conveying speed of the cardboard is set slower than conveying speed of a plain paper. That is, rotating rate (linear velocity) of the photosensitive drum in a case of the cardboard is set slower than rotating rate in a case of the plain paper. If the rotating rate of the photosensitive drum is slow, there is a problem that image flow occurs. The image flow is a phenomenon that water-soluble discharge product (e.g. an oxide, such as NOx) is adhered to the surface of the photosensitive drum, and accordingly, the toner image like a flow is formed on the surface.
This phenomenon remarkably occurs especially in a case there the photosensitive drum is an amorphous silicon photoreceptor with high hardness. In a case where the photosensitive drum is an organic photoreceptor, if discharge product is adhered, because the surface of the photosensitive drum is shaven by a cleaning blade, and then, a new face tends to be made, such a problem is hardly caused.
The image flow is caused in a situation that a surface resistance of the photosensitive drum is decreased when moisture is adhered to the discharge product, and accordingly, a surface charge flows on the surface to become ununiformity. Moreover, the surface charge may flow an exposed part of the photosensitive drum.
Accordingly, as a time between charging and exposing and a time between exposing and developing are lengthened, the image flow occurs more remarkable. That is, as the rotating rate of the photosensitive drum becomes slower, the image flow occurs more remarkable. Therefore, as the rotating rate of the photosensitive drum becomes slower, it is necessary to more improve cleaning performance of the photosensitive drum by the cleaning device.
For example, there is an image forming apparatus increasing an amount of the toner fed from the developing device to the photosensitive drum in a case where rotating rate of the photosensitive drum is varied. If the amount of the toner fed to the photosensitive drum is increased, an amount of the toner removed by the cleaning device is increased. As a result, much toner is fed to the cleaning roller and thickness of the toner layer made on the cleaning roller becomes thick, and then, performance grinding the surface of the photosensitive drum is improved.
In addition, there in another image forming apparatus heightening rotating rate of a rubbing roller (the cleaning roller) in image forming operation in comparison with rotating rate of the photosensitive drum and heightening rotating rate of the rubbing roller in non-image forming operation in comparison with the rotating rate in image forming operation. When the rotating rate of the rubbing roller is heightened in comparison with the rotating rate of the photosensitive drum, occurrence of a dash mark is restrained. When the rotating rate of the rubbing roller in non-image forming operation is heightened in comparison with the rotating rate in image forming operation, grinding force to the photosensitive drum is improved.
However, in the above-mentioned image forming apparatus, there are a problem that consumption of the toner is increased and a problem that the rotating rate of the photosensitive drum becomes unstable and an image noise of a striped pattern (a jitter noise) occurs. Moreover, there is a problem that rate control of the rubbing roller is complicated in a case where the rotating rate of the photosensitive drum is varied according to thickness of the sheet.